The embodiments disclosed herein relate generally to micro-electro-mechanical system (MEMS) attenuators and more particularly to variable optical attenuators.
The telecommunications industry is undergoing dramatic changes with increased competition, relentless bandwidth demand, and a migration toward more data-centric network architectures. First generation point-to-point wave division multiplex systems have eased the traffic bottleneck in the backbone portion of a network. As a new cross-connect architecture moves the technology closer to the subscriber side of the network, operators are challenged to provide services at the optical layer, calling for more flexible networks that switch, attenuate and reroute wavelengths. This is placing great emphasis and demand for wavelength agile devices.
The need to provide services “just in time” by allocation of wavelengths, and further migration of the optical layer from the high-capacity backbone portion to the local loop, is driving the transformation of the network toward an all optical network in which basic network requirements will be performed in the optical layer.
The optical network is a natural evolution of point-to-point dense wavelength division multiplexing (DWDM) transport to a more dynamic, flexible, and intelligent networking architecture to improve service delivery time. The main element of the optical network is the wavelength (channel), which will be provisioned, configured, routed, attenuated and managed in the optical domain. Intelligent optical networking will be first deployed as an “opaque” network in which periodic optical-electrical conversion will be required to monitor and isolate signal impairments. Longer range, the optical network will evolve to a “transparent” optical network in which a signal is transported from its source to a destination entirely within the optical domain.
A key element of the emerging optical network is an optical add/drop multiplexer (OADM). An OADM will drop or add specific wavelength channels without affecting the through channels. Fixed OADMs can simplify the network and readily allow cost-effective DWDM migration from simple point-to-point topologies to fixed multi-point configurations. True dynamic OADM, in which reconfiguration is done in the optical domain without optical-electrical conversion, would allow dynamically reconfigurable, multi-point DWDM optical networks. This dynamically reconfigurable multi-point architecture is slated to be the next major phase in network evolution, with true OADM an enabling network element for this architecture.
On chip integration of optical switching and planar light circuits has the potential to greatly reduce the size and manufacturing costs of multi-component optical equipment such as Variable Optical Attenuators (VOAs). Current costs for Variable Optical Attenuators (VOAs) are significant, limiting their use to long-haul optical telecommunications networks. In order to extend their use into the metropolitan network the cost will need to be decreased by an order of magnitude without sacrificing performance.
One solution in particular to decreasing cost is through the integration of components, where the primary cost savings will be in packaging. A number of approaches are being pursued for optical integration using Planar Light Circuit (PLC) technologies. The majority of approaches use a silica-on-silicon platform with the VOA formed from the integration of silica Arrayed Waveguide Gratings (AWG's) for multiplexing and demultiplexing, with Thermo-Optic (TO) attenuators for performing the add/drop and pass of the demultiplexed signal. The use of a low-index contrast silica-on-silicon platform severely limits the yield of these components due to the requirement for uniform thick oxide films over large areas to form the waveguides. The use of TO attenuators limits the extensibility due to high-power requirements and thermal cross-talk.
A number of different materials and switching technologies are being explored for fabricating chip-scale photonic lightwave circuits such as AWG's for demultiplexers and multiplexers, Variable Optical Attenuators (VOA's) and Reconfigurable Optical Add-Drop Multiplexers (ROADMs). The main material platforms include silica wafers, silica-on-silicon substrates using both thin film deposition and wafer bonding techniques, polymer waveguides defined on silicon substrates, and silicon-on-insulator substrates. The main switching technologies include Mach-Zehnder interferometers based on either a thermo-optic or electro-optic effect, and MEMS mechanical waveguide switches and attenuators.
While silica waveguides have optical properties that are well matched to the optical properties of conventional single mode fibers, and thus couple well to them, they require thick cladding layers due to the low index of refraction contrast between the waveguide core and cladding materials, making them difficult to fabricate using planar processing techniques for fabrication and integration with other on-chip optical devices. The low index of refraction contrast, Δn, between core and cladding also requires large bending radii to limit optical loss during propagation through the photonic lightwave circuit, leading to large chip footprints and low die yields (<50%).
In addition, silica based waveguide attenuators are typically based on Mach-Zehnder interference using thermo-optic effects, that have a limited Extinction Ratio (ER) of around 25–30 dB, require significant power due to the low thermo-optic coefficient of silica, have problems with thermal cross-talk between the different optical channels and have a sinusoidal rather than a digital optical response.
What is needed is a Silicon-On-Insulator (SOI) platform for monolithically integrating optical, mechanical and electrical functions. The use of a silicon platform enables fabrication of components using the vast infrastructure and process development available for semiconductor IC manufacturing at silicon foundries. By fabricating the MEMS switches, attenuators and waveguides in the same material, single crystal silicon, there are no stress and strain issues as exist with heterogeneous materials sets such as silica-on-silicon. Fabrication in silicon also allows for integration with CMOS microelectronics for control and sensing capabilities, and for free-carrier plasma dispersion effects to enable signal leveling using integrated VOA's. The high index contrast of silicon (n=3.5) enables the ridge waveguide structures to make tight turns with minimum optical bending loss, decreasing overall chip size to centimeter dimensions.
An optical micro-electro-mechanical system (MEMS) combination cantilever beam optical switch and attenuator is herein disclosed below. In one embodiment the optical MEMS attenuator is used as an M×N optical signal switching system. The optical MEMS attenuator comprises a plurality of optical waveguides formed on a flexible cantilever beam platform for switching optical states wherein the state of the optical attenuator is changed by a system of drive and latch actuators. The optical MEMS device utilizes a latching mechanism in association with a thermal drive actuator for aligning the cantilever beam platform. In use the optical MEMS device may be integrated with other optical components to form planar light circuits (PLCs). When attenuators and PLCs are integrated together on a silicon chip, compact higher functionality devices, such as Reconfigurable Optical Add-Drop Multiplexers (ROADMs), may be fabricated.
Disclosed in embodiments herein is a methodology for providing a micro-electro-mechanical system variable optical attenuator, comprising providing a fixed optical waveguide, providing a movable optical waveguide which may be brought into substantial alignment with the fixed optical waveguide, and misaligning the movable optical waveguide relative to the fixed optical waveguide in a manner controlled such that any optical signal passing through the fixed and movable waveguides is attenuated by some variably desired amount.
Also disclosed in embodiments herein is a methodology for providing a micro-electro-mechanical system variable optical attenuator, comprising providing a single optical gap, the single optical gap further comprising a fixed optical waveguide and a movable optical waveguide which may be brought into substantial alignment with the fixed optical waveguide, and misaligning the movable optical waveguide relative to the fixed optical waveguide micro-incrementally such that any optical signal passing through the single optical gap is thereby attenuated.
Further disclosed in embodiments herein is a methodology for providing a micro-electro-mechanical system optical switch with integral variable optical attenuator, comprising providing two or more fixed optical waveguides, and providing a movable optical waveguide which may be brought into substantial alignment with any of the two or more fixed optical waveguides. This is followed by switching the movable optical waveguide to a selected one of the two or more fixed optical waveguides, and misaligning the movable optical waveguide relative to the selected one of the two or more fixed optical waveguides in a manner such that any optical signal passing through the waveguides is attenuated by some variably desired amount.